1. Field of the Invention
This present invention relates to a method and apparatus for controlling thermoplastic friction welding machines. More particularly, the present invention relates to an electromechanical method and apparatus for determining the quality of a spinwelded bond produced by a single or multiple spindle production spinwelder and further to a method and apparatus for alarming and/or ejecting products containing defective welds.
2. Background of the Invention
In the art of joining thermoplastic articles by friction welding, a device may be used which spinwelds thermoplastic axially mating sections. The sections are driven in rotation relative to each other and then axially abutted in mating relationship. In a device, such as that disclosed in U.S. Pat. No. Re 29,448, one of the two mating sections is chucked to an initial member which is brought up to speed by a rotary drive. The rotary drive is uncoupled as the sections are moved into axial abutment and the breaking of the inertia member by the axial abutment of the sections is transformed into frictional heat which welds the thermoplastic seams to each other.
The apparatus described above may typically be a part of a larger apparatus such as that disclosed in U.S. Pat. No. 3,800,376 for performing a plurality of successive operations with individual container sections.
The processing operations may typically include the dispensing of container sections and the assembly, filling and sealing of the containers. On a single platform, a plurality of spaced processing units may be rotatably mounted. Each unit will typically include a plurality of circumferentially spaced carrier stations for moving container sections or containers about the unit axis of rotation. A plurality of spaced star wheel transfer units may then be disposed intermediate and adjacent to the processing units. The star wheels receive container sections or containers from and deliver them to the processing units at transfer zones defined generally tangentially of each of the processing units and an adjacently disposed star wheel unit. A transfer unit may be rotatably mounted on the platform and may include a plurality of circumferentially spaced carrier stations for moving the container sections or containers about the axis of rotation. The circumferential spacing of the carrier station on the transfer and processing units will typically be substantially the same throughout; and the transfer and processing units are geared together for simultaneous rotation, with the carrier stations of each of the processing units and an adjacently disposed transfer unit rotating in opposite angular directions. The initial processing units will typically have dispensers for supplying individual container sections to an adjacent transfer unit.
In addition, the invention may be useful with a friction welding machine for joining thermoplastic container top and bottom parts which are moved continuously along a production line as disclosed in U.S. Pat. No. 3,759,770. Star wheel loading and unloading members incorporating suction pads for gripping the parts as they move to the holders where flutes, in at least some of the holders, communicate the suction chambers in the holders with a vacuum source, and also hold the parts during the friction welding operation may be used.
Alternatively, the invention may be useful in connection with a device such as that disclosed in U.S. Pat. No. 3,708,376 wherein a pedestal assembly for accurately receiving and positively capturing a lower thermoplastic container half when it is being transferred in to and rotated by a spin welding apparatus is disclosed. The spin welding apparatus frictionally joins the lower container half to an upper container half to form a unitary container. The lower container half is received by the pedestal assembly from a rotating star wheel transfer device which slides the lower container half onto a stage portion of the assembly. The pedestal assembly having the container half thereon is then rotated in an opposite direction from that of the star wheel transfer device. The pedestal assembly including the stage portion has a dome-shaped upper surface which cooperates with a complementary recessed bottom of the lower container half. Vacuum means are applied through a central opening in the pedestal assembly for aiding in the positive capture of the lower container half.
Other devices where the present invention may find applicability are disclosed in U.S. Pat. No. 3,216,874 to G. W. Brown; U.S. Pat. No. 3,220,908 to G. W. Brown et al; U.S. Pat. No. 3,316,135 to G. W. Brown et al; U.S. Pat. No. 3,499,068 to G. W. Brown; U.S. Pat. No. 3,607,581 to G. A. Adams; U.S. Pat. No. 3,669,809 to G. W. Brown; U.S. Pat. No. 3,701,708 to G. W. Brown et al; U.S. Pat. No. 3,708,376 to R. J. Mistarz et al; U.S. Pat. No. 3,726,748 to R. J. Mistarz et al; U.S. Pat. No. 3,726,749 to R. J. Mistarz et al; U.S. Pat. No. 3,744,212 to R. J. Mistarz et al and U.S. Pat. No. 3,847,014 to R. J. Mistarz. It will be appreciated by the artisan that the control system of the present invention and the method by which it operates can be adapted to other devices as well.
In general, during the spinwelding process, welds are produced by the stowage of kinetic energy in the driving tool. When the two functional surfaces to be welded are brought into intimate contact, the kinetic energy is dissipated in the form of heat, thus resulting in fusion or welding of the surfaces brought together.
For purposes of the description which follows, a defective weld is defined as a failure to create a bond of adequate strength, usually due to a failure of either a loss of one of the surfaces to be welded through, for instance, a missing component or an improper fit; or a mechanical failure of a driving tool or the driven position of one of the components to be welded.
The method and apparatus of the present invention is designed to detect excess rotation of a driving tool at a point in the spinweld process where the tool should be at rest.
In connection with known spinwelding devices, a need exists for accurately and instantly determining when a container weld is defective or when an accomplished container weld has fractured. In addition, there is a need to identify and remove any defective product such as a container so that it will not be utilized and its intended contents wasted. It is desirable to perform this operation accurately and automatically to maximize the production output of the overall system. In addition, it is both necessary and desirable to identify any particular piece of equipment wherein a large amount of defective containers are being produced to allow for remedial or protective action.
In addition, it is necessary to design a control system for an apparatus as noted above that can be retrofitted into existing equipment or incorporated in new units and which therefore uses a low voltage power source.